Method of making isopropyl esters of aliphatic acids



Patented Nov. 19, 1935 UNITED Sr-Arias? PATENT- orrici-z anusi v 1 OF.ALIPHA'I'IO ACIDS x'. Dl'l'llll. Application mas, use.

. Serial Ne. at

scales. (cues-.100).

The present invention concerns an improved method of making isopropylesters of aliphatic acids throuah reacting such acids .with propylene. vs It is known that oleiines having the general formula: v

a 1o R wherein R. represents an alkyl group and R. reliresents hydrogenor an alkyl group. can be re-' acted with a substantially anhydrousaliphatic acid, under snperatmospheric pressure, and in the presence ofa catalyst, to i'orm' the isopropyl ester the aliphatic acid assubstantially the sole reaction product. carried out 'at' anytemperature above. about, 75 C. and below' the temperatureat whichmaterial decomposition of the'reaction components occurs, {In practice,howevenlhave found .it

' unnecessary and inconvenient to employ a reaction temperature aboveaboutf250 C. -I have found, furthermore, that the ester product may Thereaction may be 6 t t aliphaflgacms'to mm m; 88m be distilled directlyfrom the reacted mixture I of said acids.

compound The present invention. then, congeneral formula 60 peratureabove 100 C. reaction.

operating insuch manner, polymerisation andv a-on icn-n I Y wherein Rrepresents hydrogen or an alwl group, are less reactive toward aliphaticacids. The

higher members oi" the simple oleiines (e. g. n-

' amylenes, n-hexylenes, etc. may, however, be reacted with aliphaticacids in the presence oi certalncatalysts, such as zinc chloride. toform esters of said acids. Ethylene and propylene are '25 least reactiveof all oleiines toward aliphatic acids.

Isopropyl esters have been formed by first reacting propylene withsuliuric acid at a relatively low temperature to form intermediateobtained by such method are generally low due 88 to polymerization,charring, etc., of the propyl ene by the sulfuric acid.

In British Patent 334,228, a method is described whereby propyleneis'reacted with a solution oi acetic and sulphuric acids,the'temperature'be- 4 ing maintained below C. during reaction. glB'yoperating in such manner a mixture of isopropyl alcohol'and isopropylacetateds obtained as a Product.

Suida, in U. S. PatentNo; 1.836.135, hasde- 45 scribed a methodwherebypropylene-is reacted with a dilute aqueous aliphatic acid inthe-presence o: a relatively. small quantity of sulphuric acid, thereaction mixture being -un-- der superatmospheric pressure and at'atemcharrins or" chronic reactants; are said to vhe largelyavoided.-but amixture' oi isopropyl ho] and isopropyl ester is alwaysformed. 8!. k I have now iound that. e retained.

The simple olefin having and 'thus'be separated as the practical]? puresists in an improved method of making isopropyl esters of aliphaticacids, said niethodflbe ing hereinafter fully described and particularlypointed out in'the claims.

The iollowing examples describe in detail severa! of the various ways inwhich the principle oi my invention may be practiced. 1th: to beunderstood, however. that said examples are purely illustrative and arenot to be construed as a limitation on the invention.

Example 1 a Into an iron bomb ot the rotating type were placed 120 grams(2.0 mols) of glaclal-acetlc'acid, and 10 grams (0.1 mol) oi 98 per centsulphuric 9 acid. Approximately 111 grams (2.64 mois) oi propylenewereintroduced into the bomb and the latter sealed. The bomb was'rotatedand maintained at the temperature C. during a 6 hour period. The bombwas then cooled to room 5.-

temperature and the charge removed therefrom. Excess propylene waspermitted to escape. 'Ihe reaction mixture was then traction-- allydistilled, 89.7 grams (0.88 molio! substantially pure isopropyl acetatebeing separated,

The yield of isopropyl acetate was 44' per o! theoretical, based on thequantity of acetic acid employed. No isopropyl alcohol was obme"; bombsimilar to that described in. Example i were placed grams. (2 mols) r.glacial acetic acidand 10 grams (0.1 mol). otsii.

per cent sulphurie-acid. About 193 grams (1.9

charse removed therefrom.

i pin- 9.

reaction mixture was fractionally distilled and 140 grams (1.37 mols) ofsubstantially pure iso- No isopropylalcohol was obtained.

Example 3 I Into an iron bomb were placed 148.1 grams (2.0 mols) ofsubstantially anhydrous propionic acid and 10 grams (0.1 mol)fof 98 percent sulphuric acid. About 126.3 grams (3.05 mols) of propylene werepassed into the bomb and the latter sealed. The bomb was agitated andmaintained at the temperature 125 C. during a 6 hour period. The bombwas then cooled and the charge removed. The reaction mixture was thenfractionally distilled under subatmospheric pressure, 174.5 grams (1.5mols) ofsubstantially pure isopropyl I propionate and 37 grams (0.5 mol)of propionic acid being separated. The yield of isopropyl propionate was75 per cent of theoretical,

of theoretical, based on the acid employed.

In each of the examples, approximately 0.1'

based on the quantity of propionic acid employed. Substantially u'isopropyl alcohol or other undesirableby-products were obtained.

Example 4 l Into an iron bomb were placed 176.1 grams (2 mols) ofbutyric acidiand 10 grams (0.1 mol) "grams (0.8 mol) of unreactedbutyric acid being separated. Substantially no isopropyl alcohol orother undesirable by-products were obtained. The yield of isopropylbutyrate was 60 per cent quantity of butyric mol of catalyst was usedfor every 2 mols of acid jerjnployed. Any catalytic quantity of catalyst.i m'fi however, be employed successfully. By 50' catalytic quantity ismeant a quantity of catalyst smaller that required to be chemicallyequivalentto gtliexquantity of propylene used. In practice, I prefer toemploy less than about 5 used.

In the examples, the reactants were enclosed in a bomb and were reactedunder the vapor pres-' sure of the reaction mixture at the reactiontemperature. During plant operation, however, the

' tionally distilled to separate the pure ester product applied, then,being greater than the vapor pressure of the mixture. The reactedmixture is withdrawn continuously from the reactor, fracand theunreacted propylene and aliphatic acid and the catalyst are replenishedwith fresh quantitles of propylene and the desired aliphatic acid and.are returned to the reactor. After operv atin'g in such cyclic mannerthrough several cycles, 75

an equilibrium is reached, so that thereafter the ,quantities ofpropylene and aliphatic acid added in a given cycle are converteddirectly into the desired ester product in the same cycle.

Although we prefer to employ propylene and the desired aliphatic acid inapproximately equimolecular quantities, a large excess of eitherreactant may be used without deleterious eflect.

In the examples substantially pure propylene was employed as a reactant.Impure propylene, e. g. propylene containing an appreciable quantity ofimpurities such as saturated hydrocarbons, ethylene, etc., may, however,be employed suc-' cessfully as a reactant for the preparation of iso-"propyl esters according to the present method. If the propylene containsan appreciable quantity 15 of the more reactive higher olefines, such asbutylenes, amylenes, etc., a mixture of esters will, of course, beformed. Ethylene, on the contrary, may be present in considerablequantity without reacting to form undesirable by-products, and, in 20fact, the present method afiords a convenient means for separatingethylene from other olefines.

In each of the examples, the ester product was separated from thereacted mixture through frac- .25 tional distillation of the latter. Ifan appreciable quantity of sulphuric acid has been employed as acatalyst, it may sometimes be advantageous to neutralize or remove aportion of the sulphuric acid so as to avoid charring of the organiccomponents of the mixture during dis-- tillation. I prefer to add limeto the reacted mixture when such neutralization is desired, though anyof many other basic materialasuch as sodium hydroxide, sodium carbonate,etc., may 35 be employed instead. Ordinarily, such neutralization ofexcess sulphuric acid is unnecessary, as charring may be avoided, forinstance, by carrying the last stages of the fractional distillation outunder subatmospheric presure.

Instead of separating the ester product from the reaction mixturethrough direct distillation I of the latter, the cooled reaction mixturemay, of

course, be neutralized with a basic material, washed with water, dried,and finally purified through distillation. As previously stated, suchintermediate steps ordinarilyare unnecessary in practicing my invention.I The exact pressure under which a reaction between propylene and analiphatic acid is carried out is dependent, of course, upon a number offactors, among which may be mentioned, quantity of reactants used,relative size of reactor employed, reaction temperature maintained, etc.

In general, however, I have found that the rej action will proceedsmoothly when carried out at, or above, the vapor pressure of thereaction mixture at a reaction temperature between about 75 C. and about250 C.

The present invention, in'brief, comprises reacting propylene with asubstantially anhydrous aliphatic acid in the presence of a catalyst, ata temperature preferably between about 75 and about 250 0., and undersuperatmospheric pres-- sure to form an isopropyl ester of saidaliphatic a5 acid as substantially the sole reaction product, separatingthe .isopropyl ester from the reacted mixture, and returning all othercomponents of the mixture to the reaction. v

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated'stepor steps beemployed.

- tained under superatmospheric pressure and at I therefore particularlypoint out and distinctly claim as my 'invention:'

1. Inamethodcfmakinganisopropylesterof an aliphatic acid, the step whichconsists in reactingpropylene with a substantially anhydrous saturatedaliphatic monocarboxylic acid under superatmospheric pressure, in thepresence of sulphuric acid as catalyst. I

2. In 'a method of making an isopropyl ester of an aliphatic acid. thestep which consists in reacting propylene with a substantially anhydrousaction mixture. beingjmaintained under superatsaturated aliphaticmonocarboxylic acid in the presence of sulphuric acid as catalyst, thereaction mixture being maintained under superatmospheric pressure and ata temperature between about 75 and about 250 C. during reaction.

a 3. In a method of making an isopropyl ester of w an aliphatic acid,the steps-which consist in re-' acting propylene with a substantiallyanhydrous saturated aliphatic monocarboxylic acid in the presence ofsulphuric acid as a catalyst, the remospheric pressure and at atemperature between about 75 and about 250 C. during reaction,substantially neutralizing .the free sulphuric acid in the reactionmixture, distilling the latter to sepa-' Y rate the ester producttherefrom, and returning unreacted propylene and aliphatic acid to thefirst step.

step which consists in reacting propylene with glacial acetic acid inthe presence of sulphuric acid as catalyst, the reaction mixture beingmain,- tained under superatmospheric pressure and at a temperaturebetween about 75 and about 250 C. during reaction.

s. Inamethod otmakingisoriropylacetatathe 1 steps which consist invreacting propylene with glacial acetic acid in the presence ofsulphuric acid as catalyst, the reaction mixture being main- -i..In amethod oi making isopropyl acetate, the

about the temperature 125 C. during reaction,

- fractionally distilling the reacted mixture to sep- 4 the steps whichconsist in reacting propylene with 15 substantially anhydrous propionicacid in the presence of sulphuric acid as catalyst, the reaction mixturebeing maintained under superatmospheric pressure and at about thetemperature 125 C. during reaction, fractionally distilling the 20reacted mixtureto separate isopropylpropionate therefrom, and returningunreacted components of the mixture to the first step.

8. In a method of making isopropyl butyrate, the step which consists inreacting propylene with substantially anhydrous butyric acid in thepresence 0! sulphuric acid as catalyst, the reaction mixture beingmaintained under superatmospheric-pressure and a temperature betweenabout 75 and about-250 C. during reaction.

9. Ina method of making is'opropyl butyrate, the steps which consist inreacting Propylene with substantially anhydrous but c acid in thepresence of sulphuric acid ascatalyst, the reaction" mixture beingmaintained under superatmospheric pressure and at'about the temperature125 C. during reaction, fractionally distilling the reacted mixture toseparate isopropyl butyrate thereirom, and returning unreactedcomponents or the mixture to the first step.

GPRALD n. COLEMAN.

